The EF-Hand Ca2+ Binding Protein MICU Choreographs Mitochondrial Ca2+ Dynamics in Arabidopsis
Stephan Wagner a, Smrutisanjita Behera b, Sara De Bortoli c, David C. Logan d, Philippe Fuchs a, Luca Carraretto c, Enrico Teardo c, Laura Cendron c, Thomas Nietzel a, Magdalena Füßl e, Fabrizio G. Doccula b, Lorella Navazio c, Mark D. Fricker f, Olivier Van Aken g, Iris Finkemeier e,h, Andreas J. Meyer i, Ildikò Szabò c, Alex Costa b,j and Markus Schwarzländer a,1
aPlant Energy Biology Lab, Institute of Crop Science and Resource Conservation, University of Bonn, 53113 Bonn, Germany
bDepartment of Biosciences, University of Milan, 20133 Milan, Italy
cDepartment of Biology, University of Padova, 35121 Padova, Italy
dUniversité d'Angers, INRA, Agrocampus Ouest, UMR 1345 Institut de Recherche en Horticulture et Semences, F-49045 Angers, France
ePlant Proteomics Group, Max-Planck-Institute for Plant Breeding Research, 50829 Cologne, Germany
fDepartment of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom
gARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, WA 6009, Australia
hInstitute for Plant Biology and Biotechnology, University of Münster, 48149 Münster, Germany
iDepartment Chemical Signalling, Institute of Crop Science and Resource Conservation, University of Bonn, 53113 Bonn, Germany
jInstitute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy
↵1Address correspondence to markus.schwarzlander{at}uni-bonn.de.
Source/Fonte: The Scientist
Abstract
Plant organelle function must constantly adjust to environmental conditions, which requires dynamic coordination. Ca2+ signaling may play a central role in this process. Free Ca2+ dynamics are tightly regulated and differ markedly between the cytosol, plastid stroma, and mitochondrial matrix. The mechanistic basis of compartment-specific Ca2+ dynamics is poorly understood. Here, we studied the function of At-MICU, an EF-hand protein of Arabidopsis thaliana with homology to constituents of the mitochondrial Ca2+ uniporter machinery in mammals. MICU binds Ca2+ and localizes to the mitochondria in Arabidopsis. In vivo imaging of roots expressing a genetically encoded Ca2+ sensor in the mitochondrial matrix revealed that lack of MICU increased resting concentrations of free Ca2+ in the matrix. Furthermore, Ca2+ elevations triggered by auxin and extracellular ATP occurred more rapidly and reached higher maximal concentrations in the mitochondria of micu mutants, whereas cytosolic Ca2+ signatures remained unchanged. These findings support the idea that a conserved uniporter system, with composition and regulation distinct from the mammalian machinery, mediates mitochondrial Ca2+ uptake in plants under in vivo conditions. They further suggest that MICU acts as a throttle that controls Ca2+ uptake by moderating influx, thereby shaping Ca2+ signatures in the matrix and preserving mitochondrial homeostasis. Our results open the door to genetic dissection of mitochondrial Ca2+ signaling in plants.
Received June 10, 2015.
Revised September 25, 2015.
Accepted October 15, 2015.
Published November 3, 2015.
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